Resources of a system in the LTE-R8 are divided into a two-dimension gird in the time and frequency domains, where the smallest resource unit in the time domain is an Orthogonal Frequency Division Multiplexing (OFDM) symbol, and the smallest resource unit in the frequency domain is a sub-carrier. In the LTE-R8 standard, there is a Physical Downlink Control Channel (PDCCH) in which Downlink Control Information (DCI) can be transmitted. In across-carrier scheduling, a User Equipment (UE) in a cell has to listen to a PDCCH for system information and scheduling information, where the scheduling information can signal to the UE where to receive and how to process downlink data transmitted over a scheduled component carrier.
In the LTE-R8 system, the scheduling information can be transmitted in first several OFDM symbols of a frame, and these several OFDM symbols logically used to transmit the scheduling information can be divided into several Control Channel Elements (CCEs). CCEs are the smallest resource units of which the DCI is constituted, and the number of CCEs of which the DCI is constituted is referred to the aggregation level of a PDCCH. A possible of the aggregation level of a PDCCH is 1, 2, 4 or 8, that is, a piece of integral DCI can be consisted of 1, 2, 4 or 8 CCEs.
A User Equipment (UE) is typically provided with a corresponding PDCCH search space at a specific aggregation level, and if across-carrier scheduling is adopted in the case of carrier aggregation, then the UE has to detect scheduling information of a different scheduled component carrier over the same scheduling component carrier. Thus in across-carrier scheduling, an eNB (base station) will transmit both control information of the scheduling component carrier and other control information of the scheduled component carrier to the UE over the scheduling component carrier. Thus the eNB has to divide CCEs of the scheduling component carrier into search spaces of different component carriers for concurrent transmission of scheduling information corresponding to the different component carriers. Also in order to prevent any confusion between the scheduling information of the different component carriers of the same user equipment, a Carrier Indicator Field (CIF) of 3 bits has to be further added preceding the DCI to distinguish among the different component carriers.
In the prior art the length of a CIF is 3 bits, and the value represented by the CIF identifies uniquely another component carrier scheduled by the current scheduling component carrier. Since the CIF is specified in the LTE-R10 as 3 bits ranging from 0 to 7, only 8 different component carriers in total can be represented by the CIF. Stated otherwise, when the UE determines a component carrier and subsequently receives data borne over the component carrier by calculating the CIF as in the prior art, the process can be performed only on 8 component carriers, but the UE can not determine a larger number of component carriers and subsequently receive data thereof; and furthermore there may be a relative waste of system resource because the different component carriers are characterized by the 3 bits all the time
In summary, how to determine a larger number of component carriers and correspondingly, for a base station, how to transmit scheduling information of a scheduled component carrier to a UE when there are a larger number of component carriers, and furthermore how to characterize the different component carriers while conserving the system resource are respective technical problems highly desired to be addressed.